Background and methods: It is not certain whether patients with Kawasaki disease have a higher death rate than the age-matched healthy population. We therefore undertook a study to investigate this question. Between July 1982 and December 1988, 53 collaborating treatment centers collected data on all patients who had an unequivocal new diagnosis of Kawasaki disease; patients who had recurrent disease or whose first visit to the treatment center occurred more than 14 days after the onset of symptoms were excluded. Patients were followed from the time of the first visit to the treatment center until December 31, 1989, or until death, whichever occurred first. The expected number of deaths was calculated from Japanese vital-statistics data and compared with the number observed.
Results: Of 4676 patients who met the eligibility criteria, 4608 (98.5 percent) were followed through either the end of the study or the date of death. Thirteen patients (10 boys and 3 girls) died during the study period. The number of deaths expected was 7.61 (ratio of observed to expected deaths, 1.71; 95 percent confidence interval, 0.91 to 2.92). The ratio was 2.04 (95 percent confidence interval, 0.98 to 3.76) for boys and 1.11 (95 percent confidence interval, 0.23 to 3.23) for girls. During the acute phase of the disease (the first two months after onset), the ratios of observed to expected deaths were higher: 9.86 overall (95 percent confidence interval, 3.95 to 20.31), 13.33 for boys (95 percent confidence interval, 4.89 to 29.07), and 3.85 for girls (95 percent confidence interval, 0.10 to 21.42). After the acute phase, however, both sexes had ratios of observed to expected deaths that were lower than 1, and the difference from the control population was not statistically significant.
Conclusions: The mortality rate among boys with Kawasaki disease in Japan is twice that among healthy boys of the same age, and most deaths occur within two months of diagnosis. The mortality rate among girls with the disease appears similar to that among healthy girls, although the numbers are very small.